Patent Application
20110265506
None
None
1. Field
This application relates to a predominately electrically powered HVAC system for mobile vehicles, and specifically to such a system using two separately controlled compressors.
2. Prior Art
Being alert and well-rested is important for the safety of truck drivers and others who share the road with them. Regulations in the United States and elsewhere limit the number of hours that a driver can be behind the wheel without an extended rest break. To comply with these regulations and avoid making side trips to costly and out-of-the-way motels, it is common practice for drivers to sleep in their trucks. Heavy duty trucks designed specifically for long haul operation, commonly known as Class 8 trucks in the U.S., have sleeping accommodations built into the driver's cab for this purpose.
To ensure that the driver gets a restful sleep, it is often necessary to cool or heat the sleeper cab during rest periods, just as it is during on-highway operation. Until recently, this was accomplished by simply leaving the engine idling and using the engine-powered air conditioning and heating system. While this accomplishes the goal of maintaining a comfortable cab temperature, it does so at a substantial fuel cost to the truck operator and generates a great deal of air pollution. For this reason, many developed countries have recently banned the practice of extended engine idling. Without the ability to use the engine-driven heating and cooling system in rest stops, a new market has developed for what is known in the industry as no-idle HVAC systems. At present, manufacturers install these no-idle HVAC systems in addition to the standard engine-driven HVAC systems. Buying, installing and maintaining two HVAC systems on every truck adds an exceptional financial burden but the prior art does not provide a commercially acceptable, single system, alternative.
Because the regulations prevent running the vehicle propulsion engine when the truck is not on the road, it is necessary for these no-idle system to use an alternate source of power from the engine-drive alternator. Initially, the new systems were powered by a small, non-propulsion internal combustion (IC) engine which drove the air conditioning compressor either directly by belt, or indirectly through an electric generator. Because the IC engine produced a significant amount of waste heat, it could also provide heating in cold climates either directly through a thermal transfer loop, or indirectly though resistance heating.
In the past few years a number of no-idle air conditioning systems have been introduced that operate from electric energy stored in batteries. The batteries are then recharged by the vehicle alternator charging system once the vehicle returns to on-highway operation. Most of these systems can also operate directly from the utility grid, known in the industry as “shore power”, at times when such a connection is available. These electrically powered systems are highly desirable and generally preferred over other types because they completely eliminate the need to run any type of engine during the sleep period.
The systems of the prior art are all powered by batteries operating at the same voltage as the vehicle's main electrical system—typically 12 vdc. These batteries are recharged from the same engine-drive alternator that supplies the rest of the rest of the electrical load. This reliance on a low-voltage power source becomes a serious physical and financial limitation when trying to increase the cooling capacity of these systems to the degree that would be required if they were to replace the engine-driven systems for on-highway use.
As stated, all of the prior art generates and stores motive electric power at low voltage. However, three different systems are used to regulate, and in some cases transform, that low voltage power for use by the air conditioning systems. In the first type of system, the compressor requires high voltage AC input power. To supply this type of power, the low voltage DC power from the vehicle power system source 16 enters 12 vdc aux. battery 54 which is electrically connected to a DC-AC inverter/charger 51. The 12 vdc power is converted to 115 vac which is the input power required by the system. When these systems are connected to the utility grid, they can be run directly from the supplied power. This type of system typically uses a single-speed compressor. It operates at relatively high efficiency from utility power but less efficiently from DC power due to the single-speed operation and the power conversion losses associated with inverting low-voltage DC power to high voltage AC power. A block diagram of an input power system typical of this type of system is shown in
In a second type of system, the compressor operates from high-voltage DC power. In these systems, vehicle power system source 16 is connected directly to truck 12 vdc battery 53. Low voltage power may flow bidirectionally to a second source of power, 12 vdc aux. battery 54. Low voltage power from one or both of these two sources is conveyed to a DC-DC converter 55 which boosts voltage to approximately 350 vdc. Shore power is accommodated by using a conventional AC-DC battery charger 56 to supply low-voltage DC to the input side of the system. These systems use a variable-speed compressor which affords them better operating efficiency but requires complex control electronics. By operating the compressor at high voltage, the cost and size of the control system can be reduced due to the lower operating current. However, these advantages are largely offset by the cost, complexity and inefficiency associated with converting all system power from a low-voltage DC source. A block diagram of an input power system typical of this type of system is shown in
A third type of system uses a compressor which is powered from low-voltage DC power. As with the other systems, low voltage DC power is produced by vehicle power system source 16 and stored in a first power source truck 12 vdc battery 53 and a second power source 12 vdc aux battery 54. The compressor, which is typically driven by a variable-speed permanent magnet motor, operates directly from the low voltage DC. For shore power operation, AC power from the utility grid 17 is rectified and bucked to a lower voltage through an AC-DC charger 56. This type of system avoids the DC-DC conversion costs and losses associated with the second type of system described above. However, these advantages are offset by the high running current of the power electronics and wiring which are required to power the low-voltage compressor. A block diagram of an input power system typical of this type of system is shown in
The mobile electric HVAC systems of the prior art are intended to provide cooling when the truck is in a rest stop, generally away from a utility grid connection and with the engine turned off. As such, they are optimized to provide as much cooling power as possible using only motive power supplied from one or more banks of batteries. Once the rest period is over and the truck returns to on-highway operations, the truck alternator replaces the energy which the system has used during the engine-off period. Because the systems operate from stored energy, it naturally follows that their operating time and cooling capacity is limited by the amount of energy stored, the rate at which the energy is consumed and by the rate at which the stored energy can be replaced. In the prior art, these three factors limit maximum capacity and run time of these systems to a level so low that they are unsatisfactory for on-highway HVAC use.
While it is theoretically possible to increase the size of the battery bank to allow the systems to operate for a longer period of time, in practice, this has serious limitations. Carrying too large a battery bank reduces the amount of profit-generating freight that a truck can carry. This, combined with the cost of buying and maintaining a large battery bank, makes large batteries highly undesirable.
The fact that the prior art is designed to operate from a low-voltage DC power source is a further limitation on the maximum cooling power that can be cost-effectively obtained from these systems. Present day truck alternators, typically rated at 130 amps, are strained just to provide sufficient power to replace the power that was consumed in sleeper cab cooling. Adding on-highway air conditioning capability would mean drawing even more power from the alternator.
The power required to recharge a large battery bank combined with the power required to provide the 26,000+ btu/hr typically needed for on-highway air conditioning could easily exceed 5 kW. At 12 v, this means the alternator would need to reliably supply over 400 amps. Making matters still worse is the fact that truck alternators typically put out only 30% of their full rated power when the truck is operating at slow speeds in heavy traffic. Considering this, if 5 kW of input power is required to power the cooling system and to recharge the batteries, a truck operating in heavy traffic at slow speeds would need an alternator with a capacity rated at over 1,330 amps-10× the rating of the alternators commonly used today. Even if such alternators were available, such high current is highly undesirable since generating, controlling and wiring is heavier and more expensive for low-voltage/high-current than it is for higher voltage and lower current.
When the system design does not permit the use of higher input voltage, one way to reduce the amount of current required of the alternator is to reduce the amount of power the system uses when it is running. In U.S. Pat. No. 6,889,762, Zeigler et al. attempts to reduce the size of the battery bank by using an Intelligent Power Generation Management system. This system modulates the speed of the compressor when the propulsion engine is not running and operates the compressor at a minimum speed to extend the duration of operation. Less power is used but less cooling is produced. Therefore, this method is not helpful in a system intended to provide both on-highway and no-idle functionality.
Cooling systems whose capacity closely matches that of the load, are more energy efficient. Many battery-powered no-idle systems take advantage of this fact and increase their efficiency by varying the speed of the compressor so that the system produces the exact amount of cooling required. If, for some reason, the system cannot vary the compressor speed over a sufficiently wide range, the cooling capacity becomes disproportionate to the load and an excessive amount of power is consumed. As will be described below, this becomes yet another serious deficiency in the prior art when the systems are scaled up to higher cooling capacities.
My own U.S. Patent Application 2009/0179080 seeks to reduce the amount of power consumed by intelligently managing the operation of a variable-speed compressor, heating components and other power consuming parts of a vehicle HVAC system. This approach relies on the ability to modulate the speed of the compressor over the full range from maximum to minimum capacity to maximize efficiency and minimize the amount of energy it consumes. The method is highly effective for reducing power consumption. However, steplessly controlling the compressor from minimum to maximum speed becomes more difficult as the cooling capacity of the system increases. This “turn-down ratio” as it is called, might typically be 6:1 in a no-idle system but would have to be 26:1 to provide the same performance in a system that operated in both no-idle and on-highway conditions.
Most no-idle air conditioning systems produce a maximum of approximately 6,000 btu/hr. In such systems it is desirable to be able to modulate this to as low as 1,000 btu/hr. A turn-down ratio of 6:1 (for example, 6,000 btu/hr to 1,000 btu/hr) is the highest that is achieved in the prior art systems and is generally the limit of readily available mass-market compressors. For these systems to be able to function as they are designed in a no-idle condition, and still meet the cooling capacity requirement for on-highway operation, they would have to be able to provide 26,000 btu/hr while still being able to be turned down to 1,000 btu/hr—a 26:1 ratio. The only alternative is to cycle the systems on/off—something which creates unstable air temperatures and consumes more energy.
In a system using only one compressor, there are two main factors which limit it to a 6:1 turn-down ratio. The first is compressor lubrication. The small air conditioning compressors used in these no-idle systems rely on centrifugal force to distribute oil within the compressor. As the compressor slows down, the oil distribution suffers. If the compressor runs too slow, insufficient oil is distributed and the compressor is destroyed due to lack of lubrication.
The second limiting factor is the fact that the present day mass market air conditioning compressors rely on the momentum of the rotating motor/compressor mass to complete a full 360 degree rotation through the compression stroke. As the compressor slows down, there is less momentum energy available to complete the rotation. A compressor built to have a higher turn-down ratio would have to make up for this reduced momentum energy by using a motor and motor control electronics (which are a necessary part of any variable-speed motor) capable of providing more driving force to the compressor. This increased capacity cost money and increases size and weight. As a result, increasing the turn-down ratio of the compressor would also make it bigger, heavier and more expensive.
The invention which is the subject of this application uniquely addresses the problem of insufficient turn-down ratio by flexibly combining multiple compressors in parallel and series configurations within a single refrigerating circuit. Only one other system is known in the prior art that uses two electric compressors—the SW Arctic 2000, made by the Indel-B company, a division of the Berloni Group in Italy. In this system, two small compressors are connected in fixed parallel operation to replace single larger compressor. This approach provides no increase in the maximum turn-down ratio and addresses none of the deficiencies described in other prior art. The SW Arctic 2000 has a maximum capacity of 6,150 btu/hr and a turn-down ratio of approximately 3:1.
For all the reasons presented above, it is clear that the mobile electric conditioning systems of the prior art suffer serious limitations which prevent them from fulfilling the need for a single, commercially viable electrically-powered HVAC system capable of providing energy efficient no-idle operation from battery power during rest periods and also, providing the much higher cooling power needed for on-highway use. These limitations include;
In accordance with one embodiment, an electrically powered mobile HVAC system which efficiently and in one system, fulfills the requirements of both maximum on-highway and minimum no-idle operating conditions.
A first embodiment of a High Ratio Mobile Electric HVAC System using R-410a refrigerant gas is illustrated in
The total capacity and relative capacity of primary compressor 10 and secondary compressor 7 may vary in different applications and is a function of the minimum and maximum cooling requirement of a particular installation, the type and range of operating conditions and the type of refrigerant used. Primary compressor motor 13 and secondary compressor motor 12 are electronically commutated variable-speed motors.
Two electrically operated valves, 3-way refrigerant liquid-gas flow control 1 and 3-way refrigerant gas flow control 15 are operably positioned within the refrigerant circuit so as to selectably provide a series or a parallel connection between primary compressor 10 and secondary compressor 7. A gas intercooler 2 is a finned tube coil refrigerant-air heat exchanger sized to efficiently dissipate at least 50% of the total heat of rejection of primary compressor 10 when the system is in a series mode at full capacity and is positioned in the refrigeration circuit downstream from primary compressor discharge 9. Check valve 14 is sized to permit at least 70% of the maximum gas volume of primary compressor 10 to pass through with minimal pressure drop, and is operably connected so as to permit gas to flow in one direction from the refrigerant circuit of primary compressor discharge 9 to the refrigerant circuit of secondary compressor discharge 6.
Condenser coil 3 is an aluminum micro-channel refrigerant-air heat exchanger sized to efficiently dissipate at least 50% of the total heat of rejection of primary compressor 10 plus 100% of the total heat of rejection of secondary compressor 7 when the system is operating in parallel mode at maximum capacity. Condenser fan 4 is an axial fan powered by an environmentally sealed, variable-speed, permanent magnet motor and is operably positioned so as to circulate air from outside an interior compartment across condenser coil 3.
Pressure buffer 5 is an open reservoir such as a tube, having a volume at least 5× the single rotation displacement of primary compressor 10 and further having an inlet port to receive gas at the top and an outlet port positioned at the bottom so as to discharge gas in a manner that avoids trapping oil. It is functionally positioned so that, when the system is operating in series mode, gas pressure pulses from primary compressor 10 are smoothed and dissipated before the gas enters secondary compressor inlet 8.
Direct expansion evaporator 24 is a finned tube refrigerant-air heat exchanger sized large enough to efficiently extract heat from the air at the maximum capacity of the system when operating at full compressor speed in parallel mode. The design is self-draining so as not to trap oil when the system is operating for an extended period of time with a single compressor running at minimum speed. Receiver 20 is sized to contain the full refrigerant charge of the system. Liquid refrigerant is metered to the evaporator by evaporator refrigerant flow control 22 which is and electronic expansion valve sized to allow full transfer of refrigerant when the system is running at maximum capacity in parallel mode but is also able to precisely maintain evaporator superheat when the system is operating with a single compressor running at minimum speed. Cooling circuit fan 23 is a forward curved impeller powered by a variable-speed permanent magnet motor and is positioned to circulate air from an interior compartment over direct expansion evaporator 24.
The Compressor Oil Equalization System shown in
Motive electrical power for the system is provided by the Inlet Power System shown in
Dynamic cell charge controller 26 and multi-cell power storage battery 19 are shown in greater detail in
Cell monitoring system 31 monitors the individual cells in multi-cell power storage battery 19 and reports conditional information such as voltage, current flow, temperature and state-of-charge and stored historical data on past charge/discharge performance to distribution control system 32. Multi-cell power storage battery 19 is has an LiFePO4 chemistry. It is comprised of 110 individual cells. Each cell has a nominal voltage of 3.2 v and a peak charge voltage of 3.65 v. Connected in series, these calls give a nominal output voltage of 350 vdc which is used to drive the compressors of the system. A second output voltage is generated by dynamically selecting a sub-bank of 8 cells giving a 24 v nominal voltage for use in powering fans, pumps, controls and valves within the system.
Continuing to reference
Therefore, the requirements of the first embodiment can be met with either with fixed static output circuits as shown in
A first embodiment of a High Ratio Mobile Electric HVAC System shown in
Intelligent control system 34 receives information from user interface 50, dynamic cell charge controller 26 and other internal and external sensors as shown in
When electrically commanded by intelligent control system 34, 3-way refrigerant liquid-gas flow control 1 and 3-way refrigerant gas flow control 15 are positioned to operably connect primary compressor 10 and secondary compressor 7 in parallel or in series. In parallel connection, a refrigerant gas such as R-410a is compressed from an evaporating pressure to a condensing pressure by primary compressor 10 and secondary compressor 7.
Looking first at the operation of primary compressor 10, gas discharged from primary compressor discharge 9 flows through two separate discharge paths. The first discharge past leads to gas intercooler 2 and through 3-way refrigerant liquid-gas flow control 1 which is intelligently positioned to provide fluid communication with the second path downstream of condenser coil 3. The second discharge path leads through check valve 14 and condenser coil 3. Therefore, in parallel operating mode, condenser coil 3 and gas intercooler 2 operate in parallel to condense the refrigerant discharge gas of primary compressor 10.
Continuing in parallel operating mode and looking now at the operation of secondary compressor 7, refrigerant gas compressed by secondary compressor 7 is discharged through secondary compressor discharge 6 into the said second discharge path of primary compressor 10. The discharged gases, now combined, and enters condenser coil 3 as described above and is condensed. The now condensed and liquified refrigerant from the first discharge path and the second discharge path combine in a common circuit which, being in fluid communication with receiver 20, allows the liquid refrigerant from both compressors to enter receiver 20.
In parallel operating mode, primary compressor 10 and secondary compressor 7 may be operated individually or simultaneous at any speed to provide the desired capacity.
Looking now at the operation of the system in series operating mode, refrigerate gas is pressurized by primary compressor 10 to an intermediate pressure, the intermediate pressure being a pressure greater than the evaporating pressure but less than the condensing pressure. Upon exiting primary compressor discharge 9, the refrigerant gas enters and is cooled by gas intercooler 2. In series operating mode, gas intercooler 2 cools and reduces the pressure of the refrigerant discharged from primary compressor 10 but does not condense it.
Upon exiting gas intercooler 10, the now cooled refrigerant gas enters a-way liquid-gas flow control 1 and is directed to pressure buffer 5. Pressure buffer 5, reduces the fluctuations in pressure that are common to the inlet and discharge lines pulsating refrigerant compressors. 3-way refrigerant gas flow control 15 is now positioned to provide fluid communication between the discharge of pressure buffer 5 and secondary compressor inlet 8.
The refrigerant gas, having been discharged from primary compressor 10 at an intermediate pressure, and having been cooled by gas intercooler 2 and pressure equalized by pressure buffer 5, enters secondary compressor 7 and is further compressed to the condensing pressure. Secondary compressor discharge 6, being in fluid communication with condenser coil 3, allows gas discharged at the condensing pressure to enter condenser coil 3 where it is cooled and liquified. The exit port of condenser coil 3, being in fluid connection with receiver 20, allows the liquid refrigerant to enter receiver 20.
From this point, the fluid path remains the same in all operating modes. Liquid refrigerant, having entered and been held in reserve in receiver 20 is discharged to evaporator refrigerant flow control 22 and selectively metered to direct expansion evaporator 24. Therein, upon receiving heat from the air of an interior compartment circulated by cooling circuit fan 23, the liquid refrigerant evaporates to a gas. The gas, now at evaporating pressure, passes through sub-cooling heat exchanger 21 and removes heat from the condensed liquid refrigerant with which it is in thermal communication.
The gas returns to the operating compressor(s) via primary compressor inlet 11 and secondary compressor inlet 8. The source of gas returning to secondary compressor inlet 8 is determined by 3-way refrigerant gas flow control 15 which is positioned by the intelligent control system 31 to source gas from gas intercooler 2 in a series operating mode and from direct expansion evaporator 24 in a parallel operating mode.
In a heating mode, heat enters a liquid heat transfer loop as shown in
Operation of the Input Power System shown in
A second power source is independent power source 18 has an output voltage higher than that of main vehicle power system source 16. It is typically fully independent but in some configurations may indirectly supply power to other vehicle systems through a DC-DC converter. In this embodiment it is an engine-driven alternator outputting power at 48 vdc nominal. It may also be a regulated or unregulated permanent magnet generator or an auxiliary power source such as an internal combustion engine-powered generator, fuel cell or solar array
A third power source is utility grid power source 17 which, originating as 115 vac power, is rectified to 170 vdc power. All three sources of power may or may not be available at the same time. Dynamic cell charge controller 26 receives 200 and prioritizes 201 all power sources as shown in the Logic Flow Chart of
Having now selected a preferred power source, dynamic cell charge controller 26 measures the actual input voltage of the source 202. For example, main vehicle power system source 16 has a nominal voltage of 12 vdc but a precise voltage of 13.10 vdc. Individual cells of multi-cell power storage battery 19 each require a charge voltage of 3.65 v and have a float voltage of 3.20 v. To determine the number of cells in the charge set 204, the precise power source voltage (13.10 v) is divided by the charge voltage of an individual cell (3.65v). The number of cells in the charge set is equal to the whole number of the sum (3).
As power is drawn from multi-cell power storage battery 19, the voltage of the individual cells and the series connected battery falls. For many reasons such as manufacturing variances and internal resistance, the voltage of some cells will fall faster than others. Cell monitoring system 31 uses real-time cell voltage, current flow and temperature in conjunction with historical performance data from previous charge/discharge cycles, to determine and report the state of charge of each cell to distribution control system 32. The cells are then prioritized for charging 209 so that the cells with the lowest state of charge are charged first.
Distribution control system 32 turns on and off MOSFET circuits 33 so as to allow current to flow to the cells in the charge set(s). In many cases, the total charge voltage available exceeds the optimum charge voltage of a charge set. Similarly, individual cells in a charge set may require different charge voltages based on variance their state of charge. To adjust the charge voltage of each cell, distribution control system 32 commands the corresponding MOSFET circuit 33 to be partially turned on rather than fully turned on. A partially turned on MOSFET adjusts the voltage to the cell or, in some embodiments to the charge set, by acting as a variable resistor according to the more or less fully turned on by varying the strength of the gate drive circuit.
Because all input power sources have a limit on the amount of current that can safely be drawn, distribution control system 32 increases or decreases the number of charge set of cells that are charged at any one time so that the optimum amount of total power is drawn from the input power source.
In operation, Input Power System of
Two output voltages are produced by making two different series connections to the cells of multi-cell power storage battery 19. A high voltage of 350 vdc is produced by a series connection of 110 individual cells. A low voltage of 24 vdc is produced by a series connection of 8 individual cells. The high voltage is used to efficiently power high power components such as primary compressor 10 and secondary compressor 7 at a low current. The low voltage is used to safely power low power devices such as 3-way flow controls 1, 15 and 39, circulating pump 40 and fans 23, 39 and 4 as well as other electronic control and mechanical devices.
The series connections to multi-cell power storage battery 19 which are required to produce the two output voltages may be either static or dynamic. Two static output connections are shown in
A further benefit of the dynamic output voltage system is that the real-time and logged historical voltage and current data from output voltage control monitoring system 59 can be used in conjunction with similar data from cell monitoring system 31 on the charge side to further understand and monitor the condition of the individual cells. Additionally, the output voltage can be altered in real time in response to changing conditions. For example, in some types of motors and control circuits it is more efficient to use a lower or higher voltage as the load and/or speed changes. In a system using controllable output voltage, the voltage of one or more output circuits can be changed to optimize efficiency or to replace expensive control circuits on certain types of devices.
A second embodiment of a High Ratio Mobile Electric HVAC System is shown in
The Input Power System is as shown in
The operation of the input power system can be better understood in reference to
System layout and the operating of three compressors is otherwise as shown in
A third embodiment of an Input Power System is shown in
In the third embodiment, input power to air conditioner 52 and the subject invention is supplied through dynamic cell charge controller 26 and multi-cell power storage battery 19 as described in the first embodiment. It may also be supplied under certain operating conditions directly from alternator/generator 58. In still other operating conditions it may be flexibly supplied by a combination of both. For example, if alternator/generator 58 is an unregulated permanent magnet generator it is a characteristic of the technology to have a higher or lower voltage when the rotational speed is changed or when the load is changed. In such a case the output voltage of multi-cell power storage battery 19 may be dynamically adjusted relative to the output voltage of alternator/generator 58 by including a greater of lesser number of cells in the series string. By changing the output voltage of multi-cell power storage battery 19 relative to alternator/generator 58, the percentage of the total power which may be drawn from each is controlled. Alternately, the number of cells in series connection and, subsequently, the output voltage of multi-cell power storage battery 19 may be constant and control provided by altering the output of alternator/generator 58.
Continuing in reference to
The fourth embodiment is shown in
In view of the limitations of the prior art, there is a need for a mobile electric HVAC system which can optimally meet the cooling requirements of both on-highway and no-idle operation. The invention described in this application;
Accordingly, the reader will see that the High Ratio Mobile Electric HVAC System of the various embodiments can be used to energy-efficiently and cost-effectively meet all of the HVAC needs of a vehicle in both a resting no-idle period and in on-highway operation. It uses an independent power source which can receive power from, but is not limited by, the vehicle's main electrical system. It can achieve variable-speed in a stepless and continuous manner over virtually any range of cooling capacities making it fully compatible with large and small vehicles regardless of operational environment. Furthermore, the subject HVAC system;
Although the description above contains many specific details, these should not be construed as limiting the scope of the embodiments. For example, there are many different types of compressors that can be used such as scroll, reciprocating, rolling piston, swash plate, centrifugal and variations on these designs. Similarly, the type of on-board power sources include direct-drive, gear-driven and belt-drive generators and alternators of many types as well as fuel cells on other less conventional sources of power. In electric or hybrid-electric vehicles, these power sources could also include stored or non-stored energy used to propel the vehicle.
Thus, the scope of the embodiments should be determined by the appended claims and their legal equivalents rather than by the examples given.
